The invention herein concerns lymphokines, a class of proteins originally extracted in impure form from lymphocytes, and believed to have anti-tumor activity. Specifically, the invention concerns a homogeneous preparation of the human lymphokine, lymphotoxin, and a process for preparing it.
Lymphokines are biologically active, hormone-like peptides or proteins produced by stimulated lymphocytes. The properties and functions of these lymphokines, including those exhibiting cytotoxic activity, have been studied extensively. Lymphotoxin is a type of lymphokine which is produced not only by mitogen or antigen stimulated lymphocytes, but also by cell lines which are grown in tissue culture derived therefrom.
Lymphotoxin has been implicated in the regulation of the immne system (1) and has been reported to inhibit tumor cell growth both in vivo (2-7) and in vitro (8-10). Under in vitro conditions, it is a more potent inhibitor of tumor cells than of normal ones from the same species (11-15). Also, lymphotoxin preparations have been shown to inhibit UV or chemical carcinogen induced cell transformations (16-17). The in vitro activity of lymphotoxin may be assayed by a number of methods as will be set forth hereinbelow and these methods provide convenient means for following the processes of purification of lymphotoxin from crude extracts. In vivo studies in human beings have also shown that crude preparations of lymphotoxin are effective in tumor regression (5,7).
Previous studies have been conducted with relatively impure fractions of cell supernatants prepared from lymphocytes or cell lines derived therefrom. A number of laboratories have attempted to prepare lymphotoxin in purified form, without conspicuous success (18-24). The present invention uniquely provides a homogeneous preparation of lymphotoxin proteins useful as an anti-tumor agents in mammals.